This invention relates to cooperative electronic identification systems in which the identifying agency and the object to be identified cooperate in the identification process according to a prearranged scheme. More specifically, the invention relates to systems consisting generically of an interrogator-responsor (or xe2x80x9creaderxe2x80x9d) inductively coupled to a transponder (or xe2x80x9ctagxe2x80x9d) where the reader is associated with the identifying agency and the tag is associated with the object to be identified.
Such systems are being used or have the potential of being used for identifying fish, birds, animals, or inanimate objects such as credit cards. Some of the more interesting applications involve objects of small size which means that the transponder must be minute. In many cases it is desirable to permanently attach the tag to the object which means implantation of the device in the tissues of living things and somewhere beneath the surfaces of inanimate objects.
In most cases, implantation of the tag within the object forecloses the use of conventional power sources for powering the tag. Sunlight will usually not penetrate the surface of the object. Chemical sources such as batteries wear out and cannot easily be replaced. Radioactive sources might present unacceptable risks to the object subject to identification.
One approach to powering the tag that has been successfully practiced for many years is to supply the tag with power from the reader by means of an alternating magnetic field generated by the reader. This approach results in a small, highly-reliable tag of indefinite life and is currently the approach of choice.
Electronic identification systems of the type described above are typically used to identify objects that are more or less stationary. The reader is held in close proximity to the implanted tag and the identification of the object is read out. Moving objects, even though they are constrained to travel along a specific path, may be difficult or impossible to identify with present-day readers. The problem is that in the time it takes to read out an identification code, the object may have traveled beyond the range of the reader.
The invention is an extended-range reader for use in identifying the tag of a moving object. The reader comprises a winding of conducting wire for generating an interrogating magnetic field. The winding may be either a coil assembly consisting of a plurality of coils spaced at intervals along a common axis or a solenoid. The winding is limited to those having values of D/L less than four where D is the smallest transverse dimension of the winding and L is the length. The winding is adapted to receive a structure within the winding for providing objects a passageway through the winding. The axis of the winding may be either straight or curved. To improve the magnetic field generating capability of the winding, a magnetic shunt encircling the winding can be added.
Another element of the invention is a structure within the winding for providing objects a passageway through the winding, the structure having openings for object ingress and egress. Where the structure is intended to provide a natural environment for the objects, the structure, except for the openings, can be made pervious or impervious to liquids or gases.